It is not the first time I have seen this, it happens at rare intervals. Still it is a sight that makes many people leave their houses, to come out to the street to take pictures. At wikipedia, I have found out the reason that this double rainbow seemed so special to me, “colours of a secondary rainbow are inverted compared to the primary bow” it says.
Looking at the picture again, it is obvious that this is what I have seen without knowing. Your question was the way to know, thank you 🙂

http://en.wikipedia.org/wiki/Rainbow :
Occasionally, a second, dimmer, and thicker secondary rainbow is seen outside the primary bow. Secondary rainbows are caused by a double reflection of sunlight inside the raindrops, and appear at an angle of 50°–53°. As a result of the second reflection, the colours of a secondary rainbow are inverted compared to the primary bow, with blue on the outside and red on the inside. The dark area of unlit sky lying between the primary and secondary bows is called Alexander’s band, after Alexander of Aphrodisias who first described it.